Various terms are defined in the following specification. For convenience, a Glossary of terms is provided herein, immediately preceding the claims.
Many sources of natural gas are located in remote areas, great distances from any commercial markets for the gas. Sometimes a pipeline is available for transporting produced natural gas to a commercial market. When pipeline transportation to a commercial market is not feasible, produced natural gas is often processed into conventional liquefied natural gas (LNG), at temperatures of about -162.degree. C. (-260.degree. F.) and at atmospheric pressure, for transport to market. The LNG is typically transported via specially built tanker ships, and then stored and revaporized at an import terminal near the market.
In addition to LNG transportation technology, United States Patent application Ser. No. 09/099268 (the "PLNG Container Patent Application"), having International Patent Application Number PCT/US98/12726 and International Publication Number WO 98/59085 and entitled "Improved System for Processing, Storing, and Transporting Liquefied Natural Gas", describes containers and transportation vessels for storage and marine transportation of pressurized liquefied natural gas (PLNG) at a pressure in the broad range of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and at a temperature in the broad range of about -123.degree. C. (-190.degree. F.) to about -62.degree. C. (-80.degree. F.). The PLNG Container Patent Application is hereby incorporated herein by reference. As used throughout the remainder of this application, the term "PLNG Holder" is meant to refer to any container suitable for storing and transporting PLNG, including without limitation a container as described in the PLNG Container Patent Application.
Transportation vessels or ships for transporting a fluid fuel, including without limitation LNG, PLNG, liquefied petroleum gas (LPG), or compressed natural gas (CNG), may utilize electric motor driven propellers powered by electricity from a generator driven by a diesel engine, a gas turbine, or a steam turbine. Hereinafter, any reference to a generator includes any equipment capable of generating electric power. As an example, a generator on a fluid fuel transportation vessel with electric drive propellers may have the capability to generate about 50 mega-watts (MW) of power. Typically, over 90% of this power is used to propel the transportation vessel during transit between export and import terminals. While at an import terminal during unloading operations, i.e., during delivery of fluid fuel to market, about 20% of installed electrical power capacity may be required to deliver power for cargo handling (i.e., fluid fuel containment, loading, and delivery), for the transportation vessel's utilities, and for supplying electricity needed for on-board personnel, e.g., for lighting, small appliances, and etceteras. The remaining 80% of the installed electrical power capacity is idle. Since a significant investment is required to install the required generators on the vessel, a need exists to utilize the vessel's investment that is otherwise idle during loading and unloading operations.
Additionally, other marine transportation vessels, including without limitation cargo ships and cruise ships, sometimes carry on-board generators for powering electric drive propellers. Similar to the fluid fuel transportation vessels, while such other marine transportation vessels are at port, much of the installed electrical power capacity is idle. Since a significant investment is required to install the required generators on the marine transportation vessels, a need exists to utilize the investment that is otherwise idle while such marine transportation vessels are at port.
In certain instances when a marine vessel for transporting conventional LNG is at port, it is known to shut down the generator, e.g., for repair, and transfer electric power to the vessel from an outside source. Additionally, power generation plants are sometimes located on floating barges. However, to our knowledge, currently no system or method is known for delivering excess electric power from a self propelled marine transportation vessel to an electric power grid.
Therefore, an object of this invention is to provide systems and methods suitable for utilizing the excess electric power available on a marine transportation vessel while such vessel is at port. A specific object of this invention is to provide systems and methods suitable for delivering the excess electric power available on a fluid fuel transportation vessel to an electric power grid during unloading operations, i.e., during delivery of fluid fuel to market. Another specific object is to provide systems and methods suitable for delivering the excess electric power available on a fluid fuel transportation vessel to an electric power grid during loading operations. Further objects are made apparent by the following description of the invention.